1. Field of the Invention
This invention relates to timers in digital systems that have adjustable granularity, granularity which dynamically adjusts to communication conditions.
2. Description of the Related Art
In many digital systems, such as communication systems and computer systems, streams of information (data) between parties do not travel in a continuous fashion. Typical to many digital systems, the information is provided in the form of small and manageable pieces. To properly manage packets and streams of information, digital systems make use of protocols such as the transmission control protocol (TCP).
Information in a digital system can be broken down into a basic piece of data called a frame. A flow is a series of frames exchanged between two connection endpoints defined by a network address and a port number pair for each end of the connection. Typically a flow is initiated by a request at one of the endpoints for content which is accessible through the other connection endpoint. The flow that is created in response to the request consist of packets containing the requested content and control messages exchanged between the two endpoints.
Examples of exchanges of information include requests and transmission of data to and from client entities (client) and server entities (server). Typically, a client is the requesting endpoint; however, the server at times also requests information from a client. Applications of digital systems include transactions on the Internet, where the client is an individual connecting to a host's site and the host's site is considered the server. The individual requests information from the host site. Information is then transmitted along the Internet from the host site to the individual. In the case of electronic commerce on the Internet, the individual and the host site exchange various information packets with one another. The individual browses the host's site for specific products and/or services. The host site responds with availability and price of the goods and services. The individual responds with an order, which can include credit card information and shipping information.
The use of protocols allows efficient management of information and exchange over communication networks such as the Internet. Protocols are able to decide how to break up the transmission of information. As an example, using TCP, when a receiver (e.g., server) receives a request packet, the receiver sends an acknowledge packet back to the sender (e.g., client). If the sender does not receive an acknowledge packet after an allotted amount of time, TCP requires that the sender retransmit the packet. Other features of TCP allow for flow control; a receiver allows the sender to send only as much information at a time that the receiver's data buffers can store.
TCP and other communication protocols implement the use of timers. Timers are used to acknowledge control, and initiate and request (or re-initiate) transmission of information and information packets. Timers can also be implemented to control and monitor events. TCP includes, among other timers, an acknowledge timer, a round trip timer, a persist timer, and a keep alive timer. In TCP, timers can have a range of 200 milliseconds (ms) to several seconds.
Associated with each timer is the concept of granularity. Granularity relates to the number of interrupts over a defined time period. An interrupt is when a timer activates. The fewer number of interrupts over the defined time period, the lesser the granularity. In other words, if a timer activates (interrupts) 10 times over the defined time period, the granularity is lesser than if the timer activates (interrupts) 20 times over the same defined time period.
Under ideal conditions, communications between a client and a server are immediate and continuous. In other words, a client would not have to wait to be connected to a server, and information exchange is not interrupted. Practical conditions, however, include instances when connections between clients and servers are less than ideal. Using the example of the Internet, during certain times numerous clients (individuals) are accessing, or trying to access, the server (host site). The server in turn is trying to handle the requests from each of the clients. As more and more clients try to access the server, resources, in particular memory bandwidth, become constrained. An increased number of clients leads to increased congestion along the communication path (memory bandwidth). Processors handling the data flows are forced to handle numerous information flows. Processors responsible for computing received information are inundated with retransmitted packets. The retransmitted packets are packets containing information that has yet to be processed. Situations in which packets can be retransmitted are when an entity does not receive an acknowledge packet, the timer is started and after the set time the packet is retransmitted. Received packets that are yet to be processed, can be stored in memory buffers of devices; however, memory buffers are a limited resource that can be quickly filled during periods of peak network traffic. If memory buffers fill up, a retransmit can be requested, or transmission can be ceased.
Traffic related to information flows over networks, such as the Internet, varies depending on various factors. A simplistic example of congestion takes place when numerous clients are attempting to access a particular server. Factors that affect information (data) flows include the current data stream bandwidth, the number of data flows (TCP flows), the number of requests for memory access, the current network traffic, network congestion, the time of day, the season of the year, or a combination of any of the factors.
As networks become congested (i.e., experience more traffic), and resources become constrained, in particular as processors are asked to handle increased data streams (flows), connections are terminated and lost by the inability to properly service all client and server demands. Overall communication transactions are slowed with the increased congestion on the networks. Customers that are trying to purchase goods and/or services from server host sites are dropped. Dropped connections lead to frustrated customers who may decide not to continue transaction with the host site and seek business elsewhere.